1. Field of the Invention
This invention relates to a variable delay line of a distributed constant type, and in particular to an improvement of a variable delay line using a transmission line such as a microstrip line.
2. Description of the Prior Art
Since a transmission line can function as a delay line, it has been known from the past that the delay time may be varied when a variable delay line is formed by using such a transmission line by providing fixed contacts in the electroconductive path of this transmission line at certain intervals and by changing the length of the electroconductive path over which a signal travels through switchover of these fixed contacts.
Such a variable delay line of a distributed constant type has advantages in that the structure is simple and the manufacturing cost may be kept low, and it is capable of varying the delay time of a high speed signal having an extremely fast rise time, for instance less than one nanosecond.
However, in order to increase the incremental resolution of the delay time, a large number of fixed contacts must be formed in the electroconductive path of the transmission line at small intervals. Therefore, when such a variable delay line is to be reduced in size and its incremental resolution is to be increased, it is necessary to form a large number of fixed contacts in the electroconductive path at small intervals, and the formation of the fixed contacts becomes difficult. Therefore, it has been extremely difficult to achieve both reduction in the size of such a variable delay line and also increase in the incremental resolution of said delay time at the same time.